Field of the Invention
Embodiments of the present invention relate to a field of display technology, and in particular, to a light guide plate, a backlight module and a display device.
Description of the Related Art
With development and popularization of Light Emitting Diode (LED) light sources, conventional backlight sources such as Cold Cathode Fluorescent Lamp (CCFL) and illumination light sources such as fluorescent lamp or filament lamp have been gradually phased out from the market due to technical problems concerning color performance, environmental protection and power consumption. With the appearance of solid state semiconductor lighting sources, there have been significant changes in backlight and lighting industries, which not only overcomes defects of conventional light sources, but also changes user's habit of using light sources, because a LED light source belongs to one type of semiconductor light sources, and is different from conventional light sources in color characteristic and some of photoelectric characteristics. In view of these different characteristics of the LED light source, some changes should be made to the design of the LED light source, so as to adapt to applications where conventional backlight and illumination light sources have been used.
For example, a desirable LED light source should comprises three characteristics: firstly, good luminous efficiency, that is, a high brightness, and no additional heat dissipation is needed; secondly, good color applicability, that is, the color of the light source does not need to be adjusted for various applications of the illumination or backlight; finally, low cost. Since the cost of a light source accounts for 10% of a total cost of an entire system, an expensive light source will not facilitate its commercialization.
Actually, no perfect light source ever exists, for example, in backlight industry, most of backlight sources for televisions use light sources having a color temperature of 9,000 K and CIE chromaticity coordinates of (X: 0.27; Y: 0.28), while most of backlight sources for monitors use light sources having a color temperature of 6,500 K and CIE chromaticity coordinates of (X: 0.33; Y: 0.32). It is mainly because that color of a light source depends on color filter(s) of a display panel, and the color filter(s) used in the display panels varies from application to application; meanwhile, thicknesses and spacing of the color filters depend on pixels of a product, and change of the color filters relates to the design of the product and manufacturing process of the display panel; furthermore, the cost of a mask is relatively high. In other words, the panel manufacturers will not change the manufacturing processes of the color filters to obtain the characteristics of the backlight sources. Thus, many practitioners are trying to find solutions that can adapt to various color characteristics of the light sources. For example, there is proposed a solution in which a LED light source is used in combination with quantum dots: a layer of quantum dots is located on a light guide plate, so that a backlight source will has a better color tone and achieve a larger color range in CIE chromatic diagram, thereby improving color reproduction ability of a display device using the backlight module as described above.
The basic operation principle of the light guide plate provided with quantum dots thereon is shown in FIGS. 1-3. FIG. 1 shows a schematic cross sectional view along a row direction or column direction of a quantum dot array on a light guide plate in prior arts. For example, when applied to a blue light source, the quantum dots comprise red light quantum dots 1 and green light quantum dots 2, each of which has a radius of r, and the spacing between adjacent two quantum dots is 2r. When the angle of view is 0 degree (that is, the user directly faces toward to the display device, at this time, the incident angle is 90 degrees), the effective transmission spacing between two adjacent quantum dots is 2r. As shown in FIG. 2, when the incident angle is θ degrees, the effective transmission spacing between two adjacent quantum dots is 2r*sinθ. Accordingly, a diagram that represents the relationship between the incident angle θ and the effective light transmission spacing is shown in FIG. 3, where X is the light incident angle θ (unit: degree), Y is an effective light transmission spacing (unit: r) between two adjacent quantum dots.
In the proposed display device, however, when the angle of view (an included angle between a viewing point and normal of the display panel) is changed, a phenomenon of color shift occurs.
Thus, there is a need for a light guide plate and a display device that are capable of effectively eliminating the phenomenon of color shift.